Gear transmission between an input shaft and two contrarotating concentric output shafts

ABSTRACT

A device for contra-rotating two concentric shafts. One shaft is hollow in order to accommodate the other shaft. At least one drive shaft is connected to a power source and the concentric shafts are connected to each other by a geared transmission. The transmission includes one or more crown wheels which mesh with cylindrical pinions.

The invention relates to a gear transmission between an input shaft andtwo contra-rotating concentric output shafts consisting of a hollowouter shaft and an inner shaft extending through the hollow outer shaft,the input shaft being in line with and connected to the inner shaft,said gear transmission comprising a first gear rigidly connected to theinput shaft and the inner shaft, a second gear rigidly connected to thehollow outer shaft, and at least two intermediate gears meshing with thefirst and second gears and having their axes perpendicular to theconcentric shafts, thereby forming right-angle transmissions.

A gear transmission of this type is disclosed U.S. application Pat. No.4 792 314. This known gear transmission comprises a first bevel gearrigidly connected to the input shaft and the inner shaft, a second bevelgear rigidly connected to the hollow outer shaft and two diametricallyopposite intermediate bevel gears meshing with the first and secondbevel gears. Each bevel gear has substantially the same diameter, sothat the transmission ratio of each right-angle transmission issubstantially 1:1.

The object of the invention is to provide an improved gear transmissionbetween an input shaft and two contra-rotating concentric output shafts,in which the meshing gears can be adjusted easily, and which has a highload transmitting capacity due to an improved mesh of the gears.

This object is achieved by a gear transmission of the abovementionedtype which is characterized in that each right-angle transmissioncomprises a cylindrical pinion and a crown wheel meshing with saidpinion, the number of teeth of the crown wheel being at least 1.5 timesthe number of teeth of the cylindrical pinion, thus rendering atransmission ratio between the crown wheel and the cylindrical pinion ofat least 1.5.

The invention is based on the idea that in a gear transmission accordingto the invention two or more cylindrical pinions can mesh with the crownwheels, while maintaining the perfect mesh between the pinions and thecrown wheels required for a high load transmitting capacity. A geartransmission according to the invention comprising two or morecylindrical pinions and two crown wheels is compact and efficient.

DE-U-88 03 194 discloses a gear transmission in which the transmissionratio the crown wheel(s) and the cylindrical pinion is more than 1.However, this gear transmission is of another type, in which the inputshaft is not in line with the output shafts.

The invention also relates to a gear transmission between an input shaftand two contra-rotating concentric output shafts consisting of a hollowouter shaft and an inner shaft extending through the hollow outer shaft,said gear transmission comprising a first crown wheel rigidly connectedto the inner shaft, a second crown wheel rigidly connected to the outershaft and at least one intermediate cylindrical pinion meshing with thefirst and second crown wheels and having its axis perpendicular to theconcentric shafts, the input shaft being rigidly connected to thecylindrical pinion, as disclosed in DE-U-88 031 94, which ischaracterized in that the number of teeth of the first and second crownwheels is different and/or that at least two input shafts are provided,each input shaft being rigidly connected to a cylindrical pinion meshingwith the first and second crown wheels.

The invention is explained in greater detail with reference to thedrawings, in which:

FIG. 1 shows schematically a first embodiment of a gear transmissionaccording to the invention;

FIG. 2 shows schematically a second embodiment of a gear transmissionaccording to the invention;

FIG. 2a shows schematically a variation of the second embodiment;

FIG. 3 shows schematically a third embodiment of the device; and

FIG. 4 shows a variant of the embodiment according to FIG. 3.

FIG. 1 shows a hollow shaft 1 with a shaft 2 running concentricallythrough it. These concentric shafts can each be connected to, forexample, a propeller or driving screw which are driven in oppositedirections. Such driving systems are currently in increasing use inaircrafts (prop-fan) and ships.

Each of the concentric shafts 1, 2 is provided with a cylindrical pinion3, 4, said pinions having identical teeth and being meshed diametricallyopposite each other with two crown wheels 5 and 6. The two crown wheelsface each other with their teeth and rotate about a common axis 7, sothat these crown wheels rotate in opposite directions of rotation.

In the embodiment shown in FIG. 1 a drive shaft 8 is connected in arotation-free manner to the pinion 4 of the internal shaft 2. The driveshaft thus lies in line with the two concentric shafts 1, 2. It is,however, also possible to connect the drive shaft 8 in a rotation-freemanner to one of the crown wheels 5, 6, this shaft then forming an angleof 90° with the concentric shafts 1, 2. It will also be clear that it ispossible in principle to make do with only one crown wheel in theembodiment described above.

With such a design it is also possible to drive the concentric shaftswith power coming from different sources, as shown in FIG. 2a where anadditional drive 8a is shown. In this embodiment two input shafts areprovided, a first input shaft and a second input shaft, each shaft beingrigidly connected to a cylindrical pinion and meshing with first andsecond crown wheels. Instead of with the pinion 4, the two crown wheelscan also be driven directly by a different power source, in which casean accelerating transmission is obtained. It is also possible to drivethe two crown wheels by means of pinions which are meshed with the twocrown wheels, and each of which is connected in a rotation-free mannerto a drive shaft.

FIG. 2 shows a different embodiment of the invention, in which each ofthe concentric shafts is connected in a rotation-free manner to a crownwheel 9, 10. The two crown wheels face each other with their teeth andboth rotate about the common axis of the concentric shafts. The driveshaft 8 is provided with a cylindrical pinion 11 which meshes with thetwo crown wheels 9, 10. Rotation of the drive shaft 8 causes the crownwheels 9, 10, and thus the concentric shafts, to rotate in oppositedirections.

FIG. 3 shows schematically another embodiment of the device, in whicheach of the concentric shafts 1, 2 bears a crown wheel 9, 10 which isconnected to it in a rotation-free manner. The drive shaft 8 is in thiscase also connected in a rotation-free manner to the crown wheel 10, andin practice the drive shaft 8 is integral with the concentric shaft 1.Disposed between the two crown wheels 9, 10 are a number of cylindricalpinions 12 which are fitted at intervals in a freely rotating manner inan annular holder 13. This annular holder 13 is connected to a fixedpoint in the environment such as, for example, the housing of the gearedtransmission. Four of such pinions 12 are present in the embodimentshown in FIG. 3. This means that approximately 50% of the power suppliedthrough the shaft 8 passes through the shaft 1 to the front propeller14. The remaining 50% imparted via the crown wheel to the four pinions,so that each pinion transmits approximately 1/4×50×12.5% of the power tothe crown wheel 9. The total power imparted to the crown wheel 9 is thusalso approximately 50%, and it is subsequently conveyed via the hollowshaft 2 to the rear propeller 15.

It will be clear that any other desired number of pinions 12 can befitted between the two crown wheels. This design has the major advantagethat the tooth loads of the two crown wheels are reduced considerably,so that these crown wheels can be made smaller, with the result that theoverall radial dimensions of the geared transmission can be reduced

FIG. 4 shows a part of a variant of the device shown in FIG. 3, in whichthe crown wheel 9 has a larger number of teeth than the crown wheel 10,so that the propeller 15 will rotate correspondingly more slowly thanthe propeller 14. This design is particularly simple to produce by meansof crown wheels, and it need only be ensured that the pinions 12 arewide enough to permit them to mesh simultaneously with both the crownwheel 10 and the crown wheel 9. In conventional bevel gear transmissionsit is impossible to make the concentric shafts rotate at differentspeeds, at least if the shafts of the pinions have to be in line witheach other.

In FIG. 4 the annular holder 13 is also provided on the outer peripherywith a spline joint 16 which is in mesh with a corresponding splinejoint 17 of the fixed housing 18.

The main advantages of the design according to the invention comparedwith the conventional use of bevel gears are that the gearedtransmission is lighter and is of smaller radial dimensions. This isextremely important in the aircraft industry in particular. Besides,cylindrical pinions are very cheap to make, so that the possibly moreexpensive production of the crown wheels is amply made up for by this.

I claim:
 1. Gear transmission between an input shaft and two contra-rotating concentric output shafts comprising a hollow outer shaft and an inner shaft extending through the hollow outer shaft, the input shaft being in line with and connected to the inner shaft, said gear transmission comprising a first gear connected in a rotation free manner to the input shaft and the inner shaft, a second gear connected in a rotation free manner to the hollow outer shaft, and at least two intermediate gears meshing with the first and second gears and having their axes perpendicular to the concentric shafts, wherein the first and second gears are crown wheels and the intermediate gears are cylindrical pinions, the number of teeth of the crown wheel being at least 1.5 times the number of teeth of the cylindrical pinion, thus rendering a transmission ratio between the crown wheel and the cylindrical pinion of at least 1.5.
 2. Gear transmission of claim 1, wherein the number of intermediate cylindrical pinions is more than two.
 3. Gear transmission of claim 1, wherein the number of teeth of the first and second gears is different.
 4. Gear transmission between an input shaft and two contra-rotating concentric output shafts comprising a hollow outer shaft and an inner shaft extending through the hollow outer shaft, said gear transmission comprising a first crown wheel rigidly connected to the inner shaft, a second crown wheel rigidly connected to the outer shaft, at least two intermediate cylindrical pinions meshing with the first and second crown wheels and having their axes perpendicular to the concentric shafts, a first input shaft, and a second input shaft, each input shaft being rigidly connected to a cylindrical pinion meshing with the first and second crown wheels. 